Overexpression of a Wheat CCaMK Gene Reduces ABA Sensitivity of Arabidopsis thaliana During Seed Germination and Seedling Growth

Abscisic acid (ABA) plays pivotal roles in plant biotic and abiotic stress responses, where calcium ions are important second messengers. Calcium/calmodulin-dependent protein kinase (CCaMK) is essential for nodulation in legumes, but whether it will perceive calcium signals from abiotic stresses is not clear, especially in non-legume plants. Here we report the isolation and characterization of the D-genome copy of wheat CCaMK gene TaCCaMK. TaCCaMK was predominantly expressed in root tissues of wheat seedlings, and its proteins were located both on the cytoplasm membrane and in the nucleus as shown in the onion epidermis cells. Quantitative real-time reverse transcriptase polymerase chain reaction (qRT-PCR) assay showed that the expression of TaCCaMK was downregulated by ABA, as well as NaCl and PEG treatments in wheat seedling roots. A DNA fragment of 1,119 bp upstream of the start codon of the TaCCaMK gene (pTaCCaMK) was isolated by thermal asymmetric interlaced PCR (TAIL-PCR), on which six ABA-responsive cis-elements were predicted. pTaCCaMK can drive GUS reporter gene expression in the root and stem stalk of the transgenic Arabidopsis plants which can be repressed by ABA treatments, consistent with the observation in the qRT-PCR assay in wheat. Overexpressing TaCCaMK in Arabidopsis plants reduced their sensitivity to ABA treatment during seed germination and root elongation. Under high-salt conditions, the transgenic plants also conferred enhanced seed germination rate and became hypersensitive with increased chlorosis. Therefore, our data suggest that TaCCaMK is a negative regulator for ABA signaling which may participate in abiotic stress responses in wheat.